Electronic trip units (trip units) for actuating the separable contacts in a circuit breaker are well known. An electronic trip unit typically comprises voltage and current sensors that provide analog signals indicative of current or voltage in a power distribution circuit. The analog signals are converted by an A/D (analog/digital) converter to digital signals that are processed by a microcontroller. The trip unit further includes RAM (random access memory), ROM (read only memory) and EEPROM (electronic erasable programmable read only memory) all of which interface with the microcontroller. The ROM includes trip unit application code, e.g., main functionality trip setting values, including initializing parameters, boot code, and operational parameters (e.g., trip setting instructions). Operational parameters for the application code are also stored in the EEPROM. An output of the electronic trip unit actuates a trip module, such as a solenoid, that trips a mechanical operating mechanism. The mechanical operating mechanism, in turn, separates a pair of main contacts within the circuit breaker. When the contacts open, circuit current is prevented from flowing from one contact to the other, and electrical current is prevented from flowing to a load that is connected to the breaker. The electronic trip unit initiates a trip for instantaneous, short time, long time, ground fault, and manual conditions.
Circuit breakers having electronic trip units are described in U.S. Pat. No. 4,672,501 entitled “Circuit Breaker and Protective Relay Unit”. Such trip units often include a specific interface for a specific plug in module. One such example of a specific interface is a keypad along with a display for accessing the processor and for entering and changing the trip unit settings as described within U.S. Pat. No. 4,870,531 entitled “Circuit Breaker With Removable Display & Keypad”. Other functional modules cannot be plugged into the place where this specific plug is received within the electronic trip unit. Thus, in order for the operator to receive additional functions for the trip unit, the operator would have to order the additional functions prior to the electronic trip unit being shipped to the operator. The operator could not install these additional functions in the field. Accordingly, it is desirable to have an advanced electronic trip unit that overcomes the drawbacks and deficiences of the prior art.